Minitab rectifier for alternators

ABSTRACT

A diode for use in an under-the-hood automotive application has a TO 220 outline and consists of a diode die on a two piece lead frame which has a thick section to which the bottom of the die is soldered, and a thinner section which extends through a plastic housing as a connection tab and which has a forked end for easy connection to a node of a three phase bridge. The bottom of the thickened section is exposed through the insulation housing for easy connection to a d-c heat sink rail. The diode is particularly useful in applications greater than 2 KW.

RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/274,991, filed Mar. 12, 2001.

FIELD OF THE INVENTION

[0002] This invention relates to semiconductor devices and morespecifically relates to a novel diode structure for application toautomotive structures.

BACKGROUND OF THE INVENTION

[0003] Semiconductor devices are commonly used in automotiveapplications such as in three-phase bridge designs for automotivealternators. These are generally mounted in the hostile environment of“under-hood” locations. Despite this hostile environment (heat,vibration, shock forces, etc.), high reliability and thermal efficiencyare key requirements.

[0004] Button diodes of a well-known type are commonly used forautomotive alternators. Such button diodes have a cylindrical shape witha cylindrical conductive outer rim and flat top and bottom electrodeswhich are insulated from the rims, and define the cathode and anodeelectrodes of the device. These button diodes are commonly mounted ontwo separate heat sink sections which form the positive and negative d-crails for the output of the three-phase bridge circuit. The cathodeelectrodes of the diodes are mounted on the negative bus and the threeother button diodes are flipped over with their anodes mounted on thepositive bus.

[0005] Conventional button diodes have been found to be unreliable foralternator outputs above about 2 kW, which is needed for many modernautomotive alternator applications. Further, the upper-facing or freeelectrode of the button diode requires a separate clip connector forconnection to the circuit a-c output leads and to terminate either theanode or cathode terminal of the button diode.

[0006] It would be desirable to provide a diode structure which isreliable for operation in an alternator application at output powers inexcess of 2 kW, and which can be applied to existing alternatorstructures and heat sinks.

BRIEF DESCRIPTION OF THE INVENTION

[0007] In accordance with the invention, a novel alternator diode isprovided which can directly replace a button diode in an existingalternator structure, but can be reliably used for higher output power.

[0008] The novel diode of the invention consists of a diode package of aTO 220 type outline and which has an internal diode die having oneelectrode mounted to a first lead frame section and its other electrodewire bonded to an extending second lead frame tab which is insulatedfrom the first section. The die and lead frame sections are over-moldedwith a conventional plastic housing, with the bottom of the first leadframe section exposed for surface mounting and with the second and tabsection of the lead frame extending through the side wall of thehousing. The end of the second section is preferably forked to define aneasy screw or bolt connector connection to the common a-c connection.The exposed bottom surface of the first section and the extending tabare preferably metallized with a solderable finish. The die within thepackage can be mounted with the anode side up or down to define thediode to be connected to the positive or negative d-c bus respectively.

[0009] In one embodiment of the invention, the diode may be a Zenerdiode which, at 25° C. has a Zener voltage of 28/33 volts; a forwardvoltage drop of 1 volt at 100 amperes; an R junction-case of 0.6° C./W;a lead current rating greater than 75 amperes and an I_(AV) (180° Rect.)of 80 amperes at a case temperature of 125° C. This rating is suitablefor many alternator designs with outputs available above the 3 kW level.Further, the novel structure provides lower assembly costs and,critically, more reliable operation at higher power in the hostile“under-hood” environment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a circuit diagram of a known three-phase bridgealternator circuit for automotive alternator operation.

[0011]FIG. 2 is a side view of a prior art button diode.

[0012]FIG. 3 is a top view of FIG. 2.

[0013]FIG. 4 is a side view in partial cross-section, of the buttondiode of FIG. 2 mounted on a heat sink

[0014]FIG. 5 is a top view of FIG. 4.

[0015]FIG. 6 is a top view of the novel diode of the invention.

[0016]FIG. 7 is a side view of FIG. 6.

[0017]FIG. 8 is a partial cross-section of the device of FIG. 7 whenmounted on a heat sink.

[0018]FIG. 9 is a cross-section of the diode of FIGS. 6 and 7.

[0019]FIG. 10 is the first and second lead frame sections used tomanufacture a plurality of diodes of the kind shown in FIGS. 6, 7 and 9.

[0020]FIG. 11 shows a side view of FIG. 10.

[0021]FIG. 12 shows the lead frame sections of FIG. 10 after they arewelded together.

[0022]FIG. 13 is a side view of FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023]FIG. 1 is a circuit diagram of a typical alternator circuit towhich the diode of the invention may be applied. Thus, an automotivebattery may have its positive and negative terminals connected to d-cheat sink rails 20 and 21 respectively. The cathode terminals of diodes22, 23 and 24 are connected to the common heat sink rail 21 and theanode terminals of diodes 25, 26 and 27 are connected to the common heatsink rail 20. The a-c nodes 28, 29 and 30 of the three-phase bridge areconnected to the terminals of alternator motor 31 and the d-c terminals20 and 21 are connected to the field control 32 of the field winding ofthe motor 31.

[0024] The alternator diodes 22 to 27 in the prior art have been buttondiodes, having the structures shown in FIGS. 2 and 3 for the case ofdiode 22. Thus, diode 22 has a cylindrical rim 40 with top and bottomelectrodes 41 and 42 which are cathode and anode electrodesrespectively, and are symmetric with respect to one another. Aninsulation bead, such as bead 43 insulates rim 40 from electrode 41. Theanode electrode 42 is similarly insulated. A conventional silicon diodedie, not shown, is contained within the rim 40 and its top and bottomelectrodes are connected to electrodes 41 and 42 respectively.

[0025]FIGS. 4 and 5 show the manner in which diode 22 is connected tonegative heat sink rail 21. Thus, cathode 41 is soldered, or otherwiseaffixed to heat sink 21. A thin conductive spring clip 50 having anextending tab 51 is forceably clipped onto the top of diode 22 andcontacts anode electrode 42 and provides the terminal for node 28 inFIG. 1.

[0026] Each of diodes 23 and 24 are similarly connected to heat sinks 21and are arranged to have their clips connected to nodes 29 and 30respectively.

[0027] Diodes 25, 26 and 27 are similarly constructed, but these areflipped over so that their anodes 42 are fixed to heat sink 20 and theircathodes are connected to spring clips for connection to nodes 28, 29and 30 respectively.

[0028] In accordance with the present invention, diodes 22 to 27 of FIG.1 have a modified TO 220 type structure as shown in FIG. 6 and 7 fordiode 125 (which is connected at the location of diode 25 in FIG. 1).

[0029] Diode 125 has a surface mounted anode electrode 142 (FIGS. 7 and9), an extending cathode tab-type electrode 141, and an insulationhousing 160 which may be conventionally transfer molded. The extendingcathode tab 141 is forked, as shown in FIG. 6 for easy connection atnode 28 in FIG. 1.

[0030] The internal structure of diode 125 is best shown in FIG. 9.Thus, a silicon die 161 has conventional aluminum cathodes and anodeelectrodes 162 and 163 on its opposite surfaces. Anode electrode issoldered by solder mass 164 to the relatively thick first lead framesection 147. Solder mass 147 may be enclosed by insulation epoxy bead165. The top anode electrode 163 is wire bonded by wire bond 166 tocathode terminal 141.

[0031] The bottom of anode section 147 may be metallized to be easilysolderable, and the portion of cathode terminal 141 which protrudesthrough the side wall of insulation housing 160 is also metallized to besolderable. The anode section 147 may then be easily soldered to the topof heat sink 20 as shown in FIG. 8.

[0032] Each of the diodes in the locations of diodes 26 and 27 will havethe same structure as shown in FIG. 6, 7 and 9 and are also soldered tothe common heat sink 20.

[0033] The diodes in the positions of diodes 22, 23 and 24 are identicalto the diode of FIGS. 6, 7 and 9, except that the polarity is reversed.Thus, these diodes have the die 161 reversed within housing 160 in FIG.9 so that the lead frame section 147 is a cathode and section 141 is ananode.

[0034] FIGS. 10 to 13 show the novel lead frame which can be used tomake the device of FIGS. 6 to 9. Thus, in FIGS. 10 and 11, two leadframe sections 170 and 171 are shown. Lead frame section 170 is a leadframe which is used for a type D-2 pak lead frame and provides arelatively thick lead frame section for the first lead frame sections147. Such D-2 pak housings are made by International RectifierCorporation of El Segundo, Calif. The second lead frame section 171 isetched from a thin copper strip and defines the terminal elements 141 ofFIGS. 6 to 9. These two strips 170 and 171 are laser welded together asshown in FIGS. 12 and 13. Silicon die 161 are then die bonded to thelead frame sections 147 and their tops are wire bonded to sections 141.The die are oriented to have cathode electrodes 163 either down or up,as needed for the diodes in locations 22, 23, 24 or 25, 26, 27respectively. The lead frames are then overmolded with insulationplastic housing 160 and the individual segments are separated to definethe individual die.

[0035] In the above devices, both in a forward and reverseconfiguration, various metallization may be used. Thus, the wire bond toleads may employ aluminum metallizing. The solder die attach to the heatsink may employ a Ti/Ni/Ag metallization. There are also two siliconwafer types which can be used; one with an aluminum anode and a Ti/Ni/Agcathode; or a Ti/Ni/Ag anode and a Ti/Al cathode.

[0036] Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein.

What is claimed is:
 1. In an automotive d-c power source for deliveringpower in excess of 2 KW; an alternator for generating a three phase a-cvoltage; a three phase bridge connected rectifier having respectivediodes connected in the six legs of said bridge; a first set of three ofsaid diodes having one terminal connected to a positive d-c bus heatsink; a second set of three of said diodes having one terminal connectedto a negative d-c heat sink; respective pairs of said first and secondsets of diodes having second terminals connected to one another and to arespective one of said a-c phases of said alternator; each of saiddiodes comprising a flat thin silicon diode die having first and secondmain diode electrodes on its opposite respective surfaces, a lead framehaving a relatively thick conductive section which receives one of saidmain diode electrodes and which supports said die, and a relatively thinconductive section which is laterally removed from and insulated fromsaid relatively thick section, and wire bond means connecting the otherof said main diode electrodes to said relatively thin conductivesection, and a plastic insulation housing enclosing said die and atleast portions of said relatively thick and relatively thin conductivelead frame sections and said wire bond; said relatively thick conductivelead frame section having a bottom which is exposed through said plastichousing for connection to one of said d-c heat sinks; said relativelythin conductive section defining a connection tab extending through saidplastic housing and available for connection to one of said a-c phases.2. The device of claim 1, wherein each of said diodes have a TO 220 typeoutline.
 3. The device of claim 1, wherein the free end of saidrelatively thin conductive lead frame section has a forked end for boltconnection to its respective a-c phase.
 4. The device of claim 2,wherein the free end of said relatively thin conductive lead framesection has a forked end for bolt connection to its respective a-cphase.
 5. The device of claim 1, wherein said thin conductive lead framesection is bent at an angle out of its plane in regions external to saidplastic housing.
 6. The device of claim 5, wherein the free end of saidrelatively thin lead frame section has a forked end for bolt connectionto its respective a-c phase.
 7. The device of claim 1, wherein saiddiodes are zener diodes.
 8. The device of claim 6, wherein said diodesare zener diodes.
 9. A diode for application to alternators andconnectable between an alternator a-c terminal and a d-c bus heat sink;said diode comprising a flat thin silicon diode die having first andsecond main diode electrodes on its opposite respective surfaces, a leadframe having a relatively thick conductive section which receives one ofsaid main diode electrodes and which supports said die, and a relativelythin conductive section which is laterally removed from and insulatedfrom said relatively thick section and wire bond means connecting theother of said main diode electrodes to said relatively thin conductivesection, and a plastic insulation housing enclosing said die and atleast portions of said relatively thick and relatively thin lead framesections and said wire bond; said relatively thick lead frame sectionhaving a bottom which is exposed through said plastic housing forconnection to said d-c bus heat sink; said relatively thin conductivesection defining a connection tab extending through said plastic housingand connectable to said a-c terminal.
 10. The device of claim 9, whereinsaid diode has the outline of a TO 220 type device.
 11. The device ofclaim 9, wherein the free end of said relatively thin conductive leadframe section has a forked end for bolt connection.
 12. The device ofclaim 10, wherein the free end of said relatively thin conductive leadframe section has a forked end for bolt connection.
 13. The device ofclaim 9, wherein said thin conductive lead frame section is bent at anangle out of its plane in regions external to said plastic housing. 14.The device of claim 9, wherein said diode is a zener diode.
 15. A diodecomprising a flat thin silicon diode die having first and second maindiode electrodes on its opposite respective surfaces, a lead framehaving a relatively thick conductive section which receives one of saidmain diode electrodes and which supports said die, and a relatively thinconductive section which is laterally removed from and insulated fromsaid relatively thick section and wire bond means connecting the otherof said main diode electrodes to said relatively thin conductivesection, and a plastic insulation housing enclosing said die and atleast portions of said relatively thick and relatively thin lead framesections and said wire bond; said relatively thick lead frame sectionhaving a bottom which is exposed through said plastic housing forconnection to a heat sink; said relatively thin conductive sectiondefining a connection tab extending through said plastic housing andconnectable to an external terminal.
 16. The device of claim 15, whereinsaid diode has the outline of a TO 220 type device.
 17. The device ofclaim 15, wherein the free end of said relatively thin conductive leadframe section has a forked end for bolt connection.
 18. The device ofclaim 16, wherein the free end of said relatively thin conductive leadframe section has a forked end for bolt connection.
 19. The device ofclaim 15, wherein said thin conductive lead frame section is bent at anangle out of its plane in regions external to said plastic housing. 20.The device of claim 18, wherein said thin conductive lead frame sectionis bent at an angle out of its plane in regions external to said plastichousing.